The present invention relates to a resin composition for bumpers, and more particularly to a resin composition for bumpers showing excellent impact resistance, moldability and surface gloss.
Recently, bumpers for automobiles are increasingly required to be light and have excellent impact resistance, paintability, etc. and also have good surface appearance. Particularly, under the 5-mile regulations in the U.S., bumpers are required to be undamaged by impact corresponding to 5 mph, and also to be resistant to deterioration such as whitening, etc.
Bumpers are conventionally made of polyurethanes, polycarbonates, engineering plastic alloys, etc. However, these materials tend to be whitened by impact and are vulnerable to marring. In addition, they are expensive and are likely to suffer from large amounts of molding losses, resulting in poor productivity. Accordingly, alternative materials have been needed.
As resin compositions for bumpers having excellent impact resistance, moldability, surface appearance, etc., various compositions comprising ethylene-propylene block copolymers and ethylene-propylene copolymer rubbers and/or ethylene-propylene-diene terpolymer rubbers, and fillers such as talc, etc. were proposed (Japanese Patent Laid-Open Nos. 57-55952, 61-36346, 61-215643, 61-254649, 63-122752, 61-152658 and 63-172758). However, these resin compositions for bumpers are not necessarily satisfactory in moldability, because they are likely to have flow marks, and the addition of fillers results in poor surface appearance of their molded products.
Thus, an attempt was proposed to provide a resin composition for bumpers comprising a propylene-ethylene block copolymer, an ethylene-propylene copolymer rubber and a styrene-hydrogenated butadiene-styrene block copolymer rubber (SEBS), which has been partially put to practical use (Japanese Patent Laid-Open No. 62-15253).
However, this bumper material is not only poor in resistance to surface damage in spite of good surface gloss, but also has a nature of absorbing a large amount of trichloroethane. Accordingly, the trichloroethane used for painting remains in the rubber component in a large amount, and is evaporated in the subsequent baking process. Accordingly, the resulting coating surface is likely to have pin holes, providing the resulting bumpers with poor surface appearance.
As described above, the conventional bumper compositions are not necessarily satisfactory in impact resistance, mar resistance, moldability, surface gloss, solvent absorption, etc.